Non-linear Behavior of Polymer Based Composite Laminates under Cyclic Thermal Shock and Its Effects on Residual Stresses

The residual stresses in composite laminates depend on several factors including the conditions of fabricating process, property of materials, direction and lay-ups of the layers. However the thermo-elastic behavior of composite is one of the most important parameters affecting the magnitude of residual stresses. The elastic properties and residual stresses do not remain constant under cyclic thermal loading and vary in a non-linear manner. The study of these non-linear variations of modulus and strength and their effects on residual stresses in laminates while experiencing thermal load cycles is the main goal of this paper. An experimental device is designed and manufactured conveniently to exert defned thermal load cycles with different temperatures and cycle time on composite laminates. Then orthotropic glass-epoxy composite laminates made by hand lay-up are tested under cyclic thermal loading. The elastic modulus and fracture strength of the samples are measured before and  after  experiencing  defned  number  of  thermal  shocks. The  residual  stresses  in composite laminates are calculated and compared based on the actual behavior of composite and by means of a modifed classical laminate theory. The results of this study demonstrate that the non-linear behavior of composites infuences the residual stresses  signifcantly.  In  addition,  if  the  sample  becomes more  brittle,  the  residual strains remain constant; while the elasticity modulus and residual stresses decrease

Thermal transmittance of carbon nanotube networks: Guidelines for novel thermal storage systems and polymeric material of thermal interest

Among other applications, the study of thermal properties of large networks of carbon nanoparticles may have a critical impact in loss-free, more compact and efficient thermal storage systems, as well as thermally conducting polymeric materials for innovative low-cost heat exchangers. In this respect, here, we both review and numerically investigate the impact that nanotechnology (and in particular carbon-based nanostructures) may have in the near future. In particular, we focus on the role played by some geometrical and chemical parameters on the overall thermal transmittance of large complex networks made up of carbon nanotubes (CNTs), that can be potentially added as fillers to (thermally) low-conductive materials for enhancing the transport properties. Several configurations consisting of sole and pairs of single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs), characterized by different dimensions and number of C-O-C interlinks, are considered. Based on the results found in the literature and using focused simulations using standard approaches in Non-Equilibrium Molecular Dynamics (NEMD), we highlight the dependence on the particle diameter, length, overlap and functionalizations of both thermal conductivity and boundary resistance across CNTs, which are indeed the relevant quantities for obtaining composite materials with desired unusual thermal properties. We observe that CNTs with short overlap length and a few interlinks already show a remarkable enhancement in the overall transmittance, whereas further increase in the number of C-O-C connection only carries marginal benefits. We believe that much understanding has been gained so far in this field thanks to the work of chemists and material scientists, thus it is time to draw the attention of engineers active in the energy sector and thermal scientists on such findings. Our effort, therefore, is to gather in this article some guidelines towards innovative thermal systems that may be manufactured and employed in the near future for addressing a great challenge of our society: Storage and use of thermal energy

Overall thermal transmittance in carbon nanotube networks for thermal storage systems and composite materials

The study of thermal properties of large networks of carbon nanoparticles may have an important impact in loss-free, compact sorption-based thermal storage systems, as well as thermally conducting polymeric materials for innovative low-cost heat exchangers. Here, we both review and computationally investigate on the role that nanotechnology (and in particular carbon-based nanostructures) may have in the near future in thermal sciences. In particular, we focus on the role played by some geometrical and chemical parameters on the overall thermal transmittance of large complex networks made up of carbon nanotubes (CNTs), that can be potentially utilized as fillers for enhancing the transport properties of energy in (thermally) low-conductive materials. Several configurations of single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs), characterized by different dimensions and number of C-O-C interlinks, are considered. Based on the results reported in the published literature and using focused simulations by standard approaches in Non-Equilibrium Molecular Dynamics (NEMD), we aim at highlighting the dependence on the particle geometry, overlap and functionalizations of the boundary resistance across CNTs, which is known to be the relevant quantity affecting thermal properties of composite materials. We find that CNTs with short overlap length and only a few C-O-C interlinks already show a significant enhancement in the overall transmittance, whereas further increase in the number of connection generates marginal benefits. We believe that much understanding has been gained so far in this field thanks to the work of chemists and material scientists. Hence, it is time to draw the attention of engineers active in the energy sector and thermal scientists on such findings. Our effort, therefore, is to collect in this study a few guidelines that can be useful for the design of innovative thermal systems to be manufactured and employed in the near future for addressing some of the challenges in thermal energy storage (e.g. enhancing the heat rate during charging/discharging processes)

Coupling of Cyclotrons to Linacs for Medical Applications

Cyclotron and Linac technologies cover the vast majority of accelerator solutions applied to medicine. Cyclotrons with beams of H+/H-around 20 MeV are found for radioisotope production and cyclotrons with beams up to 250 MeV are widely used for protontherapy. Linacs are present in every medium-sized hospital with electron beams up to 20 MeV for radiotherapy and radioimaging. They have also recently become available as commercial products for protontherapy. The coupling of these two strong technologies enables to expand the capabilities of cyclotrons by using linacs as boosters. This opens the way to innovative accelerator systems allowing both radioisotope production and ion beam therapy (cyclinacs), new treatment techniques (high energy protontherapy) and new imaging techniques (proton radiography). This paper provides an overview of the technical challenges linked to coupling cyclotrons to linacs and the various solutions at hand